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constexpr_math.h
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constexpr_math.h
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// Copyright © 2016 zendo (734181759@qq.com). All rights reserved.
#pragma once
#include <type_traits>
namespace zendo
{
template<typename T>
constexpr T constexpr_max(T a)
{
return a;
}
template<typename T, typename U, typename...Args>
constexpr auto constexpr_max(T a, U b, Args...args)
{
return (a < b) ? constexpr_max(b, args...) : constexpr_max(a, args...);
}
template<typename T>
constexpr T constexpr_min(T a)
{
return a;
}
template<typename T, typename U, typename...Args>
constexpr auto constexpr_min(T a, U b, Args...args)
{
return (a > b) ? constexpr_min(b, args...) : constexpr_min(a, args...);
}
template<typename T, typename U, typename W>
constexpr auto constexpr_clamp(T a, U b, W c)
{
return (a < b) ? b : (c < a) ? c : a;
}
namespace detail
{
template<typename T, typename = void>
struct constexpr_abs_helper{};
template<typename T>
struct constexpr_abs_helper<T, typename std::enable_if<std::is_floating_point<T>::value>::type>
{
static constexpr T invoke(T val)
{
return (val < static_cast<T>(0)) ? (-val) : val;
}
};
template<typename T>
struct constexpr_abs_helper<T, typename std::enable_if<std::is_integral<T>::value && !std::is_same<T, bool>::value && std::is_unsigned<T>::value>::type>
{
static constexpr T invoke(T val)
{
return val;
}
};
template<typename T>
struct constexpr_abs_helper<T, typename std::enable_if<std::is_integral<T>::value && !std::is_same<T, bool>::value && std::is_signed<T>::value>::type>
{
static constexpr typename std::make_unsigned<T>::type invoke(T val)
{
return typename std::make_unsigned<T>::type((val < static_cast<T>(0)) ? (-val) : val);
}
};
}
template<typename T>
constexpr auto constexpr_abs(T val)-> decltype(detail::constexpr_abs_helper<T>::invoke(val))
{
return detail::constexpr_abs_helper<T>::invoke(val);
}
template<typename T>
constexpr T constexpr_square(T val)
{
return val * val;
}
template<typename T>
constexpr T constexpr_cube(T val)
{
return val * val * val;
}
namespace detail
{
template<typename T>
constexpr T constexpr_log2_internal(T a, T b)
{
return (b == static_cast<T>(1)) ? a : constexpr_log2_internal(a + static_cast<T>(1), b / static_cast<T>(2));
}
template<typename T>
constexpr T constexpr_log2_ceil_internal(T a, T b)
{
return a + static_cast<T>(static_cast<T>(1) << a < b ? 1 : 0);
}
}
template<typename T>
constexpr T constexpr_log2(T val)// log2(val)
{
return detail::constexpr_log2_internal(static_cast<T>(0), val);
}
template<typename T>
constexpr T constexpr_log2_ceil(T val)
{
return detail::constexpr_log2_ceil_internal(constexpr_log2(val), val);
}
template<typename T>
constexpr T constexpr_ceil(T val, T round)
{
return round == static_cast<T>(0) ? val : ((val + (val < static_cast<T>(0) ? static_cast<T>(0) : round - static_cast<T>(1))) / round) * round;
}
template<typename T>
constexpr T constexpr_pow(T base, std::size_t exp)
{
return (exp == 0) ? static_cast<T>(1) : (exp == 1) ? base : constexpr_square(constexpr_pow(base, exp / 2)) * (exp % 2 ? base : static_cast<T>(1));
}
template<typename T>
constexpr bool constexpr_is_power_of_2(T value)
{
static_assert(std::is_integral<T>::value, "Argument must be a integral type.");
return value && !(value & (value - 1));
}
template<typename T>
constexpr T constexpr_round_up_power_of_2(T value)
{
static_assert(std::is_integral<T>::value && (sizeof(T) == 4), "Argument must be a 32-bit integer type.");
--value;
value |= value >> 1;
value |= value >> 2;
value |= value >> 4;
value |= value >> 8;
value |= value >> 16;
return ++value;
}
template <typename T>
constexpr T constexpr_add_overflow_clamped(T a, T b)
{
using L = std::numeric_limits<T>;
using M = std::intmax_t;
static_assert(!std::is_integral<T>::value || sizeof(T) <= sizeof(M), "Integral type too large!");
return !std::is_integral<T>::value ? a + b : sizeof(T) < sizeof(M)
? T(constexpr_clamp(M(a) + M(b), M(L::min()), M(L::max()))) : !(a < 0) ? a + constexpr_min(b, T(L::max() - a)) : !(b < 0) ? a + b : a + constexpr_max(b, T(L::min() - a));
}
template <typename T>
constexpr T constexpr_sub_overflow_clamped(T a, T b)
{
using L = std::numeric_limits<T>;
using M = std::intmax_t;
static_assert(!std::is_integral<T>::value || sizeof(T) <= sizeof(M), "Integral type too large!");
return !std::is_integral<T>::value ? a - b : std::is_unsigned<T>::value ? (a < b ? 0 : a - b) : sizeof(T) < sizeof(M)
? T(constexpr_clamp(M(a) - M(b), M(L::min()), M(L::max()))) : (a < 0) == (b < 0) ? a - b : L::min() < b ? constexpr_add_overflow_clamped(a, T(-b)) : a < 0 ? a - b : L::max();
}
namespace detail
{
template<typename Char>
constexpr size_t constexpr_strlen_internal(const Char* str, size_t len)
{
return (*str == Char(0)) ? len : constexpr_strlen_internal(str + 1, len + 1);
}
}
template<typename Char>
constexpr size_t constexpr_strlen(const Char* str)
{
return detail::constexpr_strlen_internal(str, 0);
}
template <>
constexpr size_t constexpr_strlen(const char* str)
{
#if defined(__clang__)
return __builtin_strlen(str);
#elif defined(_MSC_VER) || defined(__CUDACC__)
return detail::constexpr_strlen_internal(str, 0);
#else
return std::strlen(str);
#endif
}
}